1. Field of the Invention
The present invention relates to a superconducting part and a manufacturing method thereof. Specifically, it relates to a superconducting part that is used as a dielectric resonator and other high-frequency electronic parts and to a manufacturing method thereof.
2. Description of the Related Art
Bi-2223 phase superconductors are Bixe2x80x94Pbxe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O oxide superconductors having a critical temperature on the order of 110 K. Such a Bi-2223 phase superconductor is formed on a substrate such as Ag or a single crystal of MgO or a ceramic oxide substrate and thereby constitutes a wire rod, current-limiting device or magnetic shielding material.
For example, a superconducting film is prepared by adding an organic vehicle to a powdered Bi-2223 phase superconductor to yield a paste for a superconducting film, applying the paste to a dielectric ceramic oxide substrate such as Ba(Sn,Mg,Ta)O3, and baking the applied paste. The resulting superconducting film includes no significant heterophase and substantially comprises a single phase at the interface between the superconducting film and the dielectric ceramic substrate.
However, the superconducting film exhibits a very high surface resistance in the vicinity of the interface with the dielectric ceramic substrate, although it exhibits a relatively low surface resistance on its surface on the opposite side to the interface, when the surface resistance is determined in a high frequency region. The high surface resistance is probably caused by a microscopic interface reaction between the superconducting film and the dielectric ceramic substrate. According to a conventional technique, therefore, the superconducting film has been baked at such decreased temperatures that the interface reaction does not adversely affect the superconducting film. In this case, however, the superconducting film is not satisfactorily formed and does not sufficiently have a low surface resistance.
After intensive investigations on the interface reaction, the present inventors found that Ba contained in the dielectric ceramic substrate diffuses in a high concentration into the superconducting film. Additionally, they found that when the substrate comprises a polycrystalline substance, a partially molten melt penetrates into the grain boundaries of the substrate.
The aforementioned superconducting film has a low critical current density of 200 A/cm2 (temperature: 77xc2x0 K, OT) even if it substantially comprises a single phase alone, indicating that the superconducting characteristics of the superconducting film are deteriorated not only in the vicinity of the interface with the dielectric ceramic substrate but also in a thickness direction, and further in a horizontal direction perpendicular to the thickness direction, of the superconducting film.
Under these circumstance, the present invention has been accomplished and an object of the present invention is to provide a superconducting part having excellent superconducting characteristics, as well as a manufacturing method of the superconducting part. Another object of the present invention is to provide a dielectric resonator having excellent superconducting characteristics.
Specifically, the present invention provides, in one aspect, a superconducting part including a ceramic oxide substrate and an oxide superconductor film, in which the ceramic oxide substrate comprises Ba, and the oxide superconductor film is formed on the ceramic oxide substrate, contains a Bixe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O phase as a major phase and comprises Ba.
By this configuration, the Ba component in the substrate does not diffuse into the superconducting film, and the superconducting film exhibits satisfactorily improved superconducting characteristics.
In another aspect, the present invention provides a method of manufacturing a superconducting part. The method includes the steps of applying a paste for a superconducting film containing an oxide superconductor powder to a ceramic oxide substrate including Ba, which oxide superconductor powder contains a Bixe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O phase as a major phase and includes Ba, and baking the paste to yield an oxide superconductor film.
This method can inhibit the diffusion of the Ba component in the ceramic oxide substrate into the superconducting film and can satisfactorily improve superconducting characteristics of the superconducting film.
In a further aspect, the present invention provides a dielectric resonator including a dielectric substrate and an oxide superconductor film electrode formed on the dielectric substrate, in which the dielectric substrate is a ceramic oxide including Ba, and the oxide superconductor film electrode is composed of an oxide superconductor film containing a Bixe2x80x94Srxe2x80x94Caxe2x80x94Cuxe2x80x94O phase as a major phase and includes Ba.
By this configuration, the Ba component in the dielectric does not diffuse into the oxide superconductor film electrode, and the oxide superconductor film electrode exhibits satisfactorily improved superconducting characteristics.